Thanking again alanw for his always-wise advice, I called UX (note, one of the very few airlines in the UK to officially post a normal landline number for reservations with no idiotic surcharges: ^ no1). No wait, no silly 'please press blahblahblah' menus. The lady on the phone was charming at first and even more charming when I continued in my rubbish Spanish (^ no2), and proceeded to give me a sketch of all the seats I could pre-book (^ no3). In the absence of any reason to think it should be a bad idea (and even though that probably makes me a snob I guess), I went for row 1 (window and aisle) for each of the four segments. Hope it was a wise choice... All in all, it reminded me of the pleasant experience of ringing an airline in the 1990s!